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    <title>clEnqueueReadImage</title>
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    <div class="refentry">
      <a id="idm1"></a>
      <div class="titlepage"></div>
      <div xmlns="" class="refnamediv">
        <a xmlns="http://www.w3.org/1999/xhtml" id="clEnqueueReadImage"></a>
        <h1>     
            clEnqueueReadImage
        </h1>
        <p>          
            Enqueues a command to read from a 2D or 3D image object to host memory. 
        </p>
      </div>
      <div class="refsynopsisdiv">
        <h2></h2>
        <div class="funcsynopsis">
          <table xmlns="" border="0" summary="Function synopsis" cellspacing="0" cellpadding="0">
            <tr valign="bottom">
              <td>
                <code xmlns="http://www.w3.org/1999/xhtml" class="funcdef">
                    <a class="link" href="scalarDataTypes.html" target="_top">cl_int</a>
 <strong class="fsfunc">clEnqueueReadImage</strong>
                (</code>
                <td><a xmlns="http://www.w3.org/1999/xhtml" class="link" href="abstractDataTypes.html" target="_top">cl_command_queue</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">command_queue</var>, </td>
              </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td><a xmlns="http://www.w3.org/1999/xhtml" class="link" href="abstractDataTypes.html" target="_top">cl_mem</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">image</var>, </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td><a xmlns="http://www.w3.org/1999/xhtml" class="link" href="enums.html#cl_bool" target="_top">cl_bool</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">blocking_read</var>, </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td>const <a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="_top">size_t</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">origin</var>[3], </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td>const <a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="_top">size_t</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">region</var>[3], </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td><a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="_top">size_t</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">row_pitch</var>, </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td><a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="_top">size_t</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">slice_pitch</var>, </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td><a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="_top">void</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">*ptr</var>, </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td><a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="_top">cl_uint</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">num_events_in_wait_list</var>, </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td>const <a xmlns="http://www.w3.org/1999/xhtml" class="link" href="abstractDataTypes.html" target="_top">cl_event</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">*event_wait_list</var>, </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td><a xmlns="http://www.w3.org/1999/xhtml" class="link" href="abstractDataTypes.html" target="_top">cl_event</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">*event</var><code>)</code></td>
            </tr>
          </table>
        </div>
      </div>
      <div class="refsect1">
        <a id="parameters"></a>
        <h2>Parameters</h2>
        <div class="variablelist">
          <dl class="variablelist">
            <dt>
              <span class="term">
                    <code class="varname">
						command_queue
                    </code>
                </span>
            </dt>
            <dd>
              <p> 
						Refers to the command-queue in which the read command will be
						queued. <code class="varname">command_queue</code> and image must be created with the same OpenCL contex 
                    </p>
            </dd>
            <dt>
              <span class="term">
                    <code class="varname">
						image
                    </code>
                </span>
            </dt>
            <dd>
              <p>
						Refers to a valid 2D or 3D image object.
                    </p>
            </dd>
            <dt>
              <span class="term">
                    <code class="varname">
						blocking_read
					</code>
				</span>
            </dt>
            <dd>
              <p>
						Indicates if the read operations are <code class="varname">blocking</code> or <code class="varname">non-blocking</code>.
					</p>
              <p>
						If <code class="varname">blocking_read</code> is <code class="constant">CL_TRUE</code> i.e. the read command is blocking, <code class="function">clEnqueueReadImage</code> does not return until the
						buffer data has been read and copied into memory pointed to by <code class="varname">ptr</code>.
					</p>
              <p>
						If <code class="varname">blocking_read</code> is <code class="constant">CL_FALSE</code> i.e. map operation is non-blocking, <code class="function">clEnqueueReadImage</code> queues a non-blocking read command and returns. The contents of the buffer that <code class="varname">ptr</code> points to cannot be used until the read command has completed. The <code class="varname">event</code> argument returns an event object which can be used to query the execution status of the read command. When the read command has completed, the contents of the buffer that <code class="varname">ptr</code> points to can be used by the application.						
					</p>
            </dd>
            <dt>
              <span class="term">
                    <code class="varname">
						origin
                    </code>
                </span>
            </dt>
            <dd>
              <p>
						Defines the (<span class="emphasis"><em>x, y, z</em></span>) offset in pixels in the image from where to read. If <code class="varname">image</code> is a 2D image object, the z value given by <code class="varname">origin</code>[2] must be 0.
                    </p>
            </dd>
            <dt>
              <span class="term">
                    <code class="varname">
						region
                    </code>
                </span>
            </dt>
            <dd>
              <p>
						Defines the (<code class="varname">width</code>, <code class="varname">height</code>, <code class="varname">depth</code>) in pixels of the 2D or 3D rectangle being read. If <code class="varname">image</code> is a 2D image object, the <code class="varname">depth</code> value given by <code class="varname">region</code>[2] must be 1.
                    </p>
            </dd>
            <dt>
              <span class="term">
                    <code class="varname">
						row_pitch                    
					</code>
                </span>
            </dt>
            <dd>
              <p> 
						The length of each row in bytes. This value must be greater than or equal to the element size in bytes * <code class="varname">width</code>. If <code class="varname">row_pitch</code> is set to 0, the appropriate row pitch is calculated
						based on the size of each element in bytes multiplied by <code class="varname">width</code>.
                    </p>
            </dd>
            <dt>
              <span class="term">
                    <code class="varname">
						slice_pitch
					</code>
				</span>
            </dt>
            <dd>
              <p>
						Size in bytes of the 2D slice of the 3D region of a 3D image being read. This must be 0 if <code class="varname">image</code> is a 2D image. This value must be greater than or equal to <code class="varname">row_pitch</code> * <code class="varname">height</code>. If <code class="varname">slice_pitch</code> is set to 0, the appropriate slice pitch is calculated based on the <code class="varname">row_pitch</code> * <code class="varname">height</code>.
					</p>
            </dd>
            <dt>
              <span class="term">
                    <code class="varname">
						ptr
					</code>
				</span>
            </dt>
            <dd>
              <p>
						The pointer to a buffer in host memory where image data is to be written to.
					</p>
            </dd>
            <dt>
              <span class="term">
                    <code class="varname">
						event_wait_list
					,</code>
					<code class="varname">
						num_events_in_wait_list
					</code>
				</span>
            </dt>
            <dd>
              <p>
						Specify events that need to complete before this particular command can be executed. If <code class="varname">event_wait_list</code> is NULL, then this particular command does not wait on any event to complete. If <code class="varname">event_wait_list</code> is NULL, <code class="varname">num_events_in_wait_list</code> must be 0. If <code class="varname">event_wait_list</code> is not NULL, the list of events pointed to by <code class="varname">event_wait_list</code> must
be valid and <code class="varname">num_events_in_wait_list</code> must be greater than 0. The events specified in <code class="varname">event_wait_list</code> act as synchronization points. The context associated with events in <code class="varname">event_wait_list</code> and <code class="varname">command_queue</code> must be the same.
                    </p>
            </dd>
            <dt>
              <span class="term">
                    <code class="varname">
						event
					</code>
				</span>
            </dt>
            <dd>
              <p>
						Returns an event object that identifies this particular read command and can be used to
						query or queue a wait for this particular command to complete. <code class="varname">event</code> can be NULL in which case it will not be possible for the application to query the status of this command or queue a wait for this command to complete. 		
					</p>
            </dd>
          </dl>
        </div>
      </div>
      <div class="refsect1">
        <a id="notes"></a>
        <h2>Notes</h2>
        <p>
Calling <code class="function">clEnqueueReadImage</code> to read a region of the image object with the <code class="varname">ptr</code> argument value set to <code class="varname">host_ptr</code> + (<code class="varname">origin</code>[2] * <code class="varname">image slice pitch</code> + <code class="varname">origin[1]</code> * <code class="varname">image row pitch</code> + <code class="varname">origin[0]</code> *
<code class="varname">bytes per pixel</code>), where <code class="varname">host_ptr</code> is a pointer to the memory region specified when the image object being read is created with <code class="constant">CL_MEM_USE_HOST_PTR</code>, must meet the following
requirements in order to avoid undefined behavior:
		</p>
        <div class="itemizedlist">
          <ul class="itemizedlist" style="list-style-type: disc; ">
            <li class="listitem" style="list-style-type: disc">		
				All commands that use this image object have finished execution before the read
				command begins execution.
			</li>
            <li class="listitem" style="list-style-type: disc">
				The <code class="varname">row_pitch</code> and <code class="varname">slice_pitch</code> argument values in <code class="function">clEnqueueReadImage</code> must be set to
				the image row pitch and slice pitch.
			</li>
            <li class="listitem" style="list-style-type: disc">
				The image object is not mapped.
			</li>
            <li class="listitem" style="list-style-type: disc">
				The image object is not used by any command-queue until the read command has
				finished execution.
			</li>
          </ul>
        </div>
      </div>
      <div class="refsect1">
        <a id="errors"></a>
        <h2>Errors</h2>
        <p>
			<code class="function">clEnqueueReadImage</code> return <span class="errorname">CL_SUCCESS</span> if the function is
			executed successfully. Otherwise, it returns one of the following errors.
		</p>
        <div class="itemizedlist">
          <ul class="itemizedlist" style="list-style-type: disc; ">
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_COMMAND_QUEUE</span> if <code class="varname">command_queue</code> is not a valid command-queue.
			</li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_CONTEXT</span> if the context associated with <code class="varname">command_queue</code> and <code class="varname">image</code> are not the same or if the context associated with <code class="varname">command_queue</code> and events in <code class="varname">event_wait_list</code> are not the same.
			</li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_MEM_OBJECT</span> if <code class="varname">image</code> is not a valid image object.
			</li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_VALUE</span> if the region being read specified by <code class="varname">origin</code> and <code class="varname">region</code> is out of bounds or if <code class="varname">ptr</code> is a NULL value.
			</li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_VALUE</span> if <code class="varname">image</code> is a 2D image object and <code class="varname">origin</code>[2] is not equal to 0 or <code class="varname">region</code>[2] is not equal to 1 or <code class="varname">slice_pitch</code> is not equal to 0.
			</li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_EVENT_WAIT_LIST</span> if <code class="varname">event_wait_list</code> is NULL and
				<code class="varname">num_events_in_wait_list</code> greater than 0, or <code class="varname">event_wait_list</code> is not NULL and <code class="varname">num_events_in_wait_list</code> is 0, or if event objects in <code class="varname">event_wait_list</code> are not valid events.
			</li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_MEM_OBJECT_ALLOCATION_FAILURE</span> if there is a failure to allocate memory for
				data store associated with <code class="varname">image</code>.
			</li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_OUT_OF_HOST_MEMORY</span> if there is a failure to allocate resources required by the
				OpenCL implementation on the host.
			</li>
          </ul>
        </div>
      </div>
      <div class="refsect1">
        <a id="specification"></a>
        <h2>Specification</h2>
        <p>
            <img src="pdficon_small1.gif" />
			
				      
            <a href="http://www.khronos.org/registry/cl/specs/opencl-1.0.pdf#page=67" target="OpenCL Spec">OpenCL Specification</a>
        </p>
      </div>
      <div class="refsect1">
        <a id="seealso"></a>
        <h2>Also see</h2>
        <p>
            <a class="citerefentry" href="clEnqueueWriteImage.html"><span class="citerefentry"><span class="refentrytitle">clEnqueueWriteImage</span></span></a>, 
			<a class="citerefentry" href="clEnqueueCopyImage.html"><span class="citerefentry"><span class="refentrytitle">clEnqueueCopyImage</span></span></a>
        </p>
      </div>
      <div xmlns="" class="refsect3" lang="en" xml:lang="en"><a xmlns="http://www.w3.org/1999/xhtml" id="Copyright"></a><h4 xmlns="http://www.w3.org/1999/xhtml"></h4><img xmlns="http://www.w3.org/1999/xhtml" src="KhronosLogo.jpg" /><p xmlns="http://www.w3.org/1999/xhtml"></p>Copyright © 2007-2009 The Khronos Group Inc. 
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and/or associated documentation files (the
"Materials"), to deal in the Materials without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Materials, and to
permit persons to whom the Materials are furnished to do so, subject to
the condition that this copyright notice and permission notice shall be included
in all copies or substantial portions of the Materials. 
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